1. Field of the Invention
The present invention relates to a numerical controller that controls a multi-axis machine tool in which a workpiece that is attached to a table is machined by at least three linear axes and one rotation axis. More particularly, the present invention relates to a numerical controller that performs speed control based on an allowable acceleration and an allowable jerk in an instructed path being a relative path of a tool with respect to a workpiece, speed control based on an allowable speed, an allowable acceleration and an allowable jerk in each driving axis, and speed control based on a tool reference point path allowable speed, a tool reference point path allowable acceleration and a tool reference point path allowable jerk in a below-described tool reference point path.
2. Description of the Related Art
In machine tools, a driving axis speed condition such as driving axis allowable speed, driving axis allowable acceleration and driving axis allowable jerk are applied to the driving axes of actual movement. Japanese Patent Application Laid-Open No. 2008-225825 discloses a configuration wherein a driving axis does not exceed an allowable speed, an allowable acceleration or an allowable jerk, through interpolation of an instructed path by working out the speed on the instructed path that satisfies these driving axis speed conditions. The time derivative of acceleration, i.e. the degree of change of acceleration, is referred to as jerk in the above document.
In Japanese Patent Application Laid-Open No. 2008-225825 above, a first derivative, a second derivative and a third derivative, which are time derivatives, are worked out for a movement distance s on an instructed path, in such a manner so as not to exceed the driving axis allowable speed, the driving axis allowable acceleration and the driving axis allowable jerk. On the basis of the first, second and third derivatives, the instructed path is interpolated by changing the distance s, and the driving axes are operated by performing then inverse kinematic conversion. However, Japanese Patent Application Laid-Open No. 2008-225825 above does not suggest the feature of performing speed control based on an instructed path allowable acceleration and an instructed path allowable jerk in an instructed path being a relative path of a tool with respect to the workpiece.
US Patent Application Publication No. 2009/0295323 discloses a technology wherein there is worked out the largest jerk (path jolt r(s)) on an instructed path that satisfies a driving axis speed condition such as driving axis allowable speed, driving axis allowable acceleration and driving axis allowable jerk; the jerk is integrated, to work out acceleration on the instructed path (path acceleration a(s)); the acceleration is integrated to work out speed on that instructed path (path speed v(s)); and the instructed path in interpolated based on that speed. However, the technology disclosed in US Patent Application Publication No. 2009/0295323 does not envisage control of a multi-axis machine tool where machining is performed in at least three linear axes and one rotation axis. Accordingly, there is no distinction between the driving axis speed and the instructed path speed, and there is no assumption that the driving axis path and the instructed path are different for the multi-axis machine tool. Accordingly, US Patent Application Publication No. 2009/0295323 does not suggest the feature of performing speed control based on an instructed path allowable acceleration and an instructed path allowable jerk in an instructed path being a relative path of a tool with respect to a workpiece, which are different from a driving axis allowable speed, driving axis allowable acceleration and driving axis allowable jerk.
International Publication WO 2011/064816 discloses a technology wherein, in a case where a driving axis path is instructed, there is performed interpolation by working out a feed speed on a driving axis path, such that the speed of a tool center point (end point of the tool), with respect to a workpiece, is an allowable speed (reference speed). However, WO 2011/064816 above does not suggest the feature of performing speed control based on an instructed path allowable acceleration and an instructed path allowable jerk in an instructed path being a relative path of a tool with respect to the workpiece.
Performing speed control in such a manner so as not to exceed a driving axis allowable speed, a driving axis allowable acceleration or a driving axis allowable jerk, is a conventional technique, as disclosed in Japanese Patent Application Laid-Open No. 2008-225825 and US Patent Application Publication No. 2009/0295323 above. Ordinarily, a driving axis allowable speed, a driving axis allowable acceleration and a driving axis allowable jerk are set, as set values, through measurement of an allowable speed, an allowable acceleration and an allowable jerk in each driving axis, during manufacture of the machine tool. That is, the driving axis allowable speed, driving axis allowable acceleration and driving axis allowable jerk are ordinarily set, as set values, for parameters and the like in the numerical controller, as machine tool conditions.
In order to perform machining of higher precision and higher quality, speed control is required also based on an instructed path allowable acceleration and an instructed path allowable jerk on an instructed path that is instructed by a machining program. In particular, there is often a large difference between the movement path of the driving axes and the instructed path, which is the travel path of the tool with respect to the workpiece during machining in a multi-axis machine tool where machining is performed in at least three linear axes and one rotation axis. Accordingly, speed control based on an instructed path allowable acceleration and an instructed path allowable jerk of a tool center point on an instructed path which is a relative path of a tool center point with respect to the workpiece and is instructed by a machining program, is an important issue in order to perform machining of higher precision and higher quality. That is because tool marks may be formed on the machined surface if acceleration and jerk in the instructed path are excessive, and grooves may be formed on account of excessive tool infeed.
An instance will be explained wherein, for example, an instructed path being a relative path with respect to a workpiece, of a tool center point that is located in a program coordinate system, is instructed by a machining program, on a program coordinate system, as illustrated in FIG. 1. The actual workpiece is disposed on a table that rotates about two rotation axes (A-axis, C-axis) such as those illustrated in FIG. 2, and is machined by a tool. In the machining program, the instructed path of the tool center point is instructed at X, Y and Z positions on the program coordinate system, the instructed path speed is instructed as a speed F and the tool direction is instructed as a rotation axis position (A-axis and C-axis position) and a tool direction vector (FIG. 1),
In this machining program, the X, Y and Z instructions are linear instructions. In actual machining, however, the X, Y and Z-axes, as driving axes, with rotational movement of the A-axis and C-axis, move tracing a curve on a machine coordinate system, as in the driving axis path of FIG. 2. Herein, the driving axes are controlled so as to move within allowable speed, allowable acceleration and allowable jerk, according to conventional technologies. However, no control is performed on the allowable acceleration and allowable jerk of the instructed path, being a relative path of the tool center point with respect to the workpiece. Therefore, large acceleration and/or jerk may occur on the path of the tool center point with respect to the workpiece, in particular at corners in the machining program and at curved portions of large curvature. In such cases, tool marks in the tool length direction may appear on the machined surface, in particular, during machining of the workpiece with the side face of the tool, and grooves may be formed on account of excessive tool infeed. Recesses may also become formed on account of excessive infeed during machining with the tool center point (FIG. 3). The driving axes operate at high speed, high acceleration and high jerk, in particular, in high-rigidity and high-speed machine tools where large allowable speed, allowable acceleration and allowable jerk are set for each driving axis. As a result, large acceleration and jerk occur also in the path of the tool center point with respect to the workpiece, and tool marks, grooves and/or recesses may be formed in such machined surfaces.
Upon machining of a workpiece with the side face of a tool, it is necessary to perform speed control based on the acceleration and jerk of the tool center point, but also speed control based on the allowable speed, allowable acceleration and allowable jerk in the tool reference point path, which is a relative path of the tool reference point with respect to the workpiece, by setting, as the tool reference point, a reference position on the tool different from the tool center point (for instance, a tool position corresponding to a machining top face) (FIG. 1 and FIG. 2). In the machining of FIG. 2, a workpiece is cut with a cutting blade at a part between a tool center point and a tool reference point. Therefore, if no speed control is performed at the tool reference point, similarly to speed control at the tool center point, then tool marks may be formed on the machined surface, and grooves or the like may be formed on account of excessive tool infeed, as in FIG. 3.